Trigeminal contribution to the head righting reflex

Abstract

The aim of the present research was to study the participation of trigeminal afferents in head righting reflexes from lateral decubitus. The degree of head righting was measured in 11 guinea pigs before and after unilateral trigeminal section and in 8 bilaterally labyrinthectomized animals before and after unilateral trigeminal neurotomy. All animals were restrained by a body-holder tube to exclude body-righting reflexes acting on the head. Some animals were also blindfolded to avoid the occurrence of optical righting reflexes. In normal animals, the degree of head righting reached a mean value of 70.7°, while after left trigeminal neurotomy, head righting from the operated side underwent a decrement of 18.5°, reaching a mean value of 52.5°. In the 8 bilaterally labyrinthectomized animals, head righting tests revealed a residual righting of 13.5°: the unilateral section of trigeminal nerve completely abolished this partial righting from the side of the sectioned nerve. On the basis of the reported results, in the guinea pig head righting, although mainly triggered by labyrinthine inputs, is also under the influence of trigeminal afferents asymmetrically stimulated by contact with the ground when the animal is placed in lateral decubitus. Thus a “trigeminal head righting reflex” has been demonstrated to contribute to the righting functions.